Process for producing cyclohexane



Feb- 1, 1966 G. E. MERRYFIELD ETAL 3,233,001

PROCESS FOR PRODUCING CYCLOHEXANE FiledJan. 25, 196s A T TURA/EVS United States Patent t p y 3,233,001 PROCESS FOR PRODUCENG CYCLOHEXANE George E. ll/lerryiieldand .lohn T. Cabbage, Bartlesville,

Okla., assignors to lzhillips Petroleum Company, a corporation of Delaware Filed Jan. 25, 1963, Ser. No. 253,926 Claims. `(Ci. Zoli-66o) This invention relates to a process and apparatus for producing high purity cyclohexane from a mixe-d stream of C6 hydrocarbons.

In the production of cyclohexane from a refinery stream of mixed C6 hydrocarbons, one of the problems involved is the separation of 2,2- and ZA-dimethylpentanes from the feed. These compounds are diicult to separate from cyclohexane and methylcyclopentane because of their close boiling points to those of cyclohexane and methylcyclopentane. This invention is concerned with a method for converting methylcyclopentane to cyclohexane which readily eliminates 2,2- and 2,4-dimethylpentanes from the C6 hydrocarbons 4being treated.

Accordingly, it is an object of the invention to provide a process for the production of high purity cyclohexane utilizing a unique method of removing 2,2- and 2,4-dimethylpentanes from a common C6 feed found in renery operations. Another object is to provide a novel process for producing high purity cyclohexane from a common renery stream containing n-hexane, cyclohexane, methylcyclopentane, benzene, and 2,2- and 2,4-dimethylpentanes, with unique removal of the dimethylpentanes. Other objects of the invention will `become apparent to one skilled in the art upon consideration yot the accompanying disclosure.

A broad aspect of the invention comprises contacting a mixed C6 feed containing n-hexane, cyclohexane, methylcyclopentane, benzene, and 2,2- and 2,4-dimethylpentanes in a hydroisomerization reaction zone with a hydroisomerization catalyst and in admixture with hydrogen so as to convert cyclohexane to methylcyclopentane, n-hexane to isohexanes, and 2,2- and 2,4-dirnethylpentanes to n-heptane and higher boiling isoheptanes; fractionating the eilluent from the hydroisomerization step to recover an overhead fraction comprising principally methylcyclopentane, n-hexane, isohcxanes, and benzene, and a bottoms fraction comprising principally cyclohexane, n-heptane, and isoheptanes; hydrogenating the overhead fraction in contact with a hydrogenation catalyst in admixture with hydrogen to convert benzene therein to cyclohexane; isomerizing the eiiluent from the hydrogenation step in contact with an isomerizing catalyst to convert n-hexane to isohexanes and to convert methylcyclopeutane to cyclohexane; fractionating the eliluent from the preceding Iisomerization step to recover an overhead fraction comprising principally isohexane, unc-onverted n-hexane, and methylcyclopentane, and a bottoms fraction comprising principally cyclohexane; and fractionating the bottoms fraction of the first fractionation step to recover an overhead fraction comprising principally cyclohexane and a 'bottoms `fraction comprising principally heptanes. The overhead fraction from the last-mentioned fractionation step, comprising principally cyclohexane, also contains impur-ities in suilicient quantity that it is recycled along with the feed to the hydroisomerization step. In this way the cyclohexane is converted to methylcyclopentane which is again reconverted to .cyclohexane and the impurities in the recycled stream are removed during the process.

The preferred hydroisomerization catalyst comprises platinum-halogen on active alumina. Other hydroisomerization catalyst maybe utilized less advantageously, however. The preferred hydrogenation catalyst comprises nickel in metallic form supported on kieselguhr. Other ICC hydrogenation catalysts supported on kieselguhr or other silica or silica-alumina supports may be utilized. Nickel may also ybe supported on other similar supports. The preferred iomerization catalyst for the isomer-ization step following the isomerization step comprises HCl-promoted Amig-hydrocarbon complex. Other active isomerization catalysts may be utilized in lieu of the aforesaid catalyst.

By passing the feed through the hydroisomerization zone, the 2,2- and 2,4-dimethylpentanes are converted to isoheptanes and normal heptane which have higher boiling points than cyclohexane. By fractionating the elliuent from the hydroisomerization zone, taking the MCP and lighter hydrocarbons overhead and the cycloiexane and heavier hydrocarbons as ythe bottoms fraction, the cyclohexane and C7s in the bottoms fraction may vbe readily fractionated to separate the cyclohexane from the Cqs, thereby eliminating the 2,2- and .2A-dimethylpentanes from the system.

A more complete understanding of the invention may be had by neference to the llow sheet shown in the schematic drawing illustrating the process.

ln the drawing, a mixed C6 feed containing n-hexane, cyclohexane, rnethylcyclopentane, benzene, and 2,2- and 2,4-dimethylpentanes, after removal of isonexanes therefrom, is passed through line it? along with hydrogen from line l2 into hydroisomerization reactor 14 which contains a platinum-halogen-alumina catalyst and is maintained preferably in the temperature range of 500 to 800 F., more desirably in the temperature range of 600 to 750 F. and under other reaction conditions which convert cyclohexane to methylcyclopentane, n-hexane to isohexanes, and 2,2- and 2,4-dirnethylpcntanes to n-heptane and isoheptanes. The reaction eliiuent is passed through line 16 into fractionator 13 which is maintained under conditions which pass the methylcyclopentane and lighter products overhead through line 20 to hydrogenation reactor 22, and a bottoms fraction comprising `cyclohexane and heptanes through line 24 to fractionator 26.

The dimethylpentanes have 4been converted to n-heptane and isoheptanes in reactor i4 and these conversion products are separated in ractionator Z6 as a bottoms traction which is recovered through line 28. The overhead traction comprising cyclohexane and other C6 and lighter hydrocarbons is passed through line 30 to line 10 as recycle to the hydroisomerization step.

Hydrogenation is effected in reactor 22 under conventional hydrogenation conditions over a nickel-kieselguhr catalyst principally to convert benzene to cyclohexane, the benzene being detrimental to the catalyst in the downstream isornerization zone. The effluent from the hydrogenation reactor 22 is passed through line 32 into isomeri- Zation reactor 34 which is maintained preferably in the temperature range of to 160 F., more desirably in a temperature range of l2() to 140 F. and is provided with an HCl-promoted aluminum chloride-hydrocarbon cornplex catalyst so as to convert n-hexane to isohexanes and methylcyclopentane to cyclohexane. The reaction effluent is passed through line 36 to fractionator 38 which is operated under conditions which take the isohexanes and lighter overhead and cyclohexane and heavier hydrocarbons as a bottoms fraction. The overhead is recovered through a line 40 and may be combined with isohexanes separated from the feed, initially; and the bottoms fraction is passed through line d2 into fractionator 44 for separation of the cyclohexane overhead which is recovered through line da and heavier hydrocarbons recovered through line 4S.

The invention is devised to maximize production of high purity cyclohexane and conversion of n-hexane to isohexanes. The hydroisomerization step converts cyclohexane to methylcyclopentaue, achieving an equilibrium ratio of about 3:1 of MCP to cyclohexane and converts n-hexane to isoliexanes, and stabilizes the resulting eflluent to remove C5 and lighter components. An important feature of this hydroisornerization step is the conversion of 2,2- and 2,4-dimethylpentanes to higher boiling isoheptanes and normal heptane which can be separated readily from cyclohexane by conventional fractionation.

The following example illustrates operation in accordance with the invention utilizing the flow of the drawing to produce a product stream of cyclohexane of more than Certain modifications of the invention will become apparent to those skilled in the art and the illustrative details disclosed are not to be construed as imposing unnecessary limitations on the invention.

We claim:

ll. A process for producing cyclohexane from a C6 hydrocarbon feed mixture containing n-liexane, cyclohexane, methylcyclopentane, benzene, and 2,2- and ZA-dimethylpentanes and treated to remove a substantial proportion of isohexanes, which comprises the steps l0 98 percent purity and `isohexanes as a separate product (l) contacting said feed without fractionation thereof stream. in a hydroisomerization zone with a hydroisomeriza- Example tion catalyst consisting essentially of Pit-halogen dis- TOWER CONDITIONS tended on active alumina and in admixture with hy- 15 drogen at a temperature in the range of 50G-800 F. Tower 18 Tower 26 Tower 38 Tower 411 S0 as to Convert (a) cyclohexane to methyleyclopentane, 'rop Temp., ii 249 250 245 250 (b) n-hexane t0 ischexanes, and Top Pressure p-Sisn---m- 40 35 40 35 c 2 2- and 2 /lf-dimeth l entane n-h ri Bottom Temp., "F 289 30o est) 30o h. h .1. p L ,S to epm e Bottom rressure,p.s.ig 49 to n 40 20 and 1s er bonne 1S0 eptanes,

(2) fractionating the eflluent from step (l) to recover REACTION CONDlTIONS (a) an overhead fraction comprising principally methylcyclopentane, n-hexane, isohexanes, ben- No.14 No.22 Nasi 26H6, and Reactor Reactor Reactor 25 (b) a bottoms fraction comprising principally cyclohexane, n-heptane, and isoheptanes and a- Pressure. psig 500 450 170 ingr amount of benzenep., 750 485 12o Space velocity, v./v./iir t( 2 n (3) hydrogenating overhead iraction (a) of step (2) in r 7! H T' v l u lype Catalyst Platinum NCL Colllncel; Contact with a hydrogenation catalyst and in adn-11X- Ilz/oil Mol Ratio 2.5 0.4 None 30 ture with hydrogen to convert benzene therein to cyclohexane;

Stream Number (V olnmes,1 Mols/Day) Combined Reactor Bottoms Bottoms Feed Recycle Feed To (14) of DMCP of DCyC (i0) (so) Reactor (14) nement (18)(24) (26)(23) (io-p30) (is) Component:

Isohexanes 1, 600 1, 600 7, 500

Normal Hexane..- 8, 044 2 8, 046 2, 146

Methyleyclopeutano. 3, G37 110 3, 747 5, 497

2,2-dimetliylpentai1e 107 23 130 27 Benzene 500 499 999 999 2,4-dirnethy1pentan 215 20 235 23 oyelohexane 1, 822 539 2, 361 611 2,2,3-trrnethy1butane 1G 18 3,3-dimethylpentane 6 6 32 2,3-dimethylpentane. 113

2-methylhexane 2 2 77 -methylhexane. 1 1 109 3-ethylpentane 9 Normal Heptane 63 63 45 Total 15, 988 1,218 17, 206 17, 206

Stream Number (V olumes,1 Mols/Day)-Continued Overhead Hydro- Isomeri- Tower Tower Tower Tower of DMCP genation zation (38) (38) (44) (44) (18) (20) Effluent Effluent Over- Bottoms Over- Bottoms (32) (as) head (40) (42) head (46) (4s Component:

Ischexanes Normal Hexane Metlilycyclopentane 2,2-dimethylpentane Benzene 2,4-dirnethylpentane Cyclohex ane 2,2,3-trimetl1ylbut 3,3-dmethylpei1tane 2,3-dimetliylpentane- 2-methylhexane. 3-methy1hexane. 3-ethylpentane Normal Heptane Total 1 Hydrogen 110W not shown, 2 Heavy reaction products.

The foregoing example is illustrative of the invention and is not to be interpreted as unnecessarily limiting the invention.

(4) isomerizing the eiiluent from step (3) in contact with an isomerizing catalyst to convert (a) n-hexane to isoliexanes, and

(b) mcthylcyclopentane to cyclohexane; (5) fractionating the etiluent from step (4) to recover (a) an overhead fraction comprising principally isollexanes, unconverted n-hexane, and methylcyclopentane, and (b) a bottoms fraction comprising principally cyclohexane; and (6) fractionating bottoms fraction (b) of step (2) to recover (a) an overhead fraction comprising principally cyclohexane and a substantial proportion of benzene, and (b) a bottoms fraction comprising principally heptanes.

2. The process of claim 1 including the step of recycling overhead fraction (a) of step (6) to step (1) to form additional methylcyclopentane from cyclohexane, the benzene in the recycled overhead fraction being passed to step (3).

3. The process of claim 1 wherein said hydrogenation catalyst of step (3) comprises nickel, and the isomerization catalyst of step (4) consists essentially of an HC1 promoted AlClg-hydrocarbon complex.

E 4. The process of claim 3 wherein the temperature in the hydroisomerization zone of step (1) is in the range of 600 to 750 F., and the temperature in isomerization step (4) is in the range of 120 to 140 F.

5. The process of claim 1 including the step of fractionating bottoms fraction (b) of step (5) to recover (a) an overhead fraction consisting of at least 98 percent cyclohexane, and (b) a bottoms fraction of heavier hydrocarbons than cyclohexane.

References Cited by the Examiner UNITED STATES PATENTS 2,382,446 8/1945 Ross et al 260-666 2,821,561 1/1958 Pevere et al. 260,-666 2,952,715 9/1960 Donaldson et al. 260--683.68 2,953,606 9/1960 Dean et al 260-666 2,999,890 9/1961 Davison 260-666 DELBERT E. GANTZ, Primary Examiner.

DANIEL E. WYMAN, Exmniner. 

1. A PROCESS FOR PRODUCING CYCLOHEXANE FROM A C6 HYDROCARBON FEED MIXTURE CONTAINING N-HEXANE, CYCLOHEXANE, METHYLCYCLOPENTANE, BENZENE, AND 2,2-AND 2,4-DIMETHYLPENTANES AND TREATED TO REMOVE A SUBSTANTIAL PROPORTION OF ISOHEXANES, WHICH COMPRISES THE STEPS (1) CONTACTING SAID FED WITHOUT FRACTIONATION THEREOF IN A HYDROISOOMERIZATION ZONE WITH A HYDROISOMERIZATION CATALYST CONSISTING ESSENTIALLY OF PT-HALOGEN DISTENDED ON ACTIVE ALUMINA AND IN ADMIXTURE WITH HYDROGEN AT A TEMPERATURE IN THE RANGE OF 500-800*F. SO AS TO CONVERT (A) CYCLOHEXANE TO METHYLCYCLOPENTANE, (B) N-HEXANE TO ISOHEXANES, AND (C) 2,2- AND 2,4-DIMETHYLPENTANES TO N-HEPTANE AND HIGHER BOILING ISOHEPTANES; (2) FRACTIONATING THE EFFLUENT FROM STEP (1) TO RECOVER (A) AN OVER HEAD FRACTION COMPRISING PRINCIPALLY METHYLCYCLOPENTANE, N-HEXANE, ISOHEXANES, BENZENE, AND (B) A BOTTOMS FRACTION COMPRISING PRINCIPALLY CYCLOHEXANE, N-HEPTANE, AND ISOHEPTANES AND A MINOR AMOUNT OF BENZENE; (3) HYDROGENATING OVERHEAD FRACTION (A) OF STEP (2) IN CONTACT WITH A HYDROGENATION CATALYST AND IN ADMIXTURE WITH HYDROGEN TO CONVERT BENZENE THEREIN TO CYCLOHEXANE; (4) ISOMERIZING THE EFFLUENT FROM STEP (3) IN CONTACT WITH AN ISOMERIZING CATALYST TO CONVERT (A) N-HEXANE TO ISOHEXANES, AND (B) METHYLCYCLOPENTANE TO CYCLOHEXANE; (5) FRACTIONATING THE EFFLUENT FROM STEP (4) TO RECOVER (A) AN OVER HEAD FRACTION COMPRISING PRINCIPALLY ISOHEXANES, UNCONVERTED N-HEXANE, AND METHYLCYCLOPENTANE, AND (B) A BOTTOMS FRACTION COMPRISING PRINCIPALLY CYCLOHEXANE; AND (6) FRACTIONATING BOTTOMS FRACTION (B) OF STEP (2) TO RECOVER (A) AN OVERHEAD FRACTION COMPRISING PRINCIPALLY CYCLOHEXANE AND A SUBSTANTIAL PROPORTION OF BENZENE, AND (B) A BOTTOMS FRACTION COMPRISING PRINCIPALLY HEPTANES. 